Optical member and lens unit

Abstract

An optical member includes a light-transmissive member, a hard coat layer covering the light-transmissive member, and an antireflection layer covering the hard coat layer. The antireflection layer is configured such that the high refractive index films and the low refractive index films are alternately stacked. The high refractive index film contains Si3N4. The low refractive index film contains SiO2. The total number of films of the high refractive index films and the low refractive index films is an even number. For each of the high refractive index film and the low refractive index film in the antireflection layer, of two adjacent films, a ratio of thickness of a thick film to thickness of a thin film is six times or less. An average reflectance of the antireflection layer in a wavelength range of 300 to 400 nm is 40% or more.

1 . An optical member comprising:
 a light-transmissive member;   a hard coat layer covering the light-transmissive member; and   an antireflection layer covering the hard coat layer,   wherein the antireflection layer is configured such that high refractive index films and low refractive index films are alternately stacked,   the high refractive index films contain Si 3 N 4 ,   the low refractive index films contain SiO 2 ,   a total number of films of the high refractive index films and the low refractive index films is an even number,   a ratio of thickness of a thick film to thickness of a thin film of two adjacent films is six times or less for each of the high refractive index films and the low refractive index films in the antireflection layer, and   an average reflectance of the antireflection layer in a wavelength range of 300 to 400 nm is 40% or more.   
     
     
         2 . The optical member according to  claim 1 , wherein the total number of films of the high refractive index films and the low refractive index films is ten or less. 
     
     
         3 . The optical member according to  claim 2 , wherein the total number of films of the high refractive index films and the low refractive index films is six or more and eight or less. 
     
     
         4 . The optical member according to  claim 1 , wherein a film located farthest from the hard coat layer in the antireflection layer is one of the low refractive index films. 
     
     
         5 . A lens unit comprising a plurality of lenses, wherein at least one lens of the plurality of lenses is the optical member according to  claim 1 . 
     
     
         6 . The lens unit according to  claim 5 , further comprising a lens barrel to which a plurality of lenses can be attached,
 Wherein the at least one lens is arranged to be exposed from the lens barrel, and   a remaining lens of the plurality of lenses is arranged in the lens barrel.